1. Field of the Invention
The present invention relates to shelf-stable, isocyanate (NCO) free urethane urea acrylate resins.
2. Description of the Prior Art
Films and coatings obtained after radiation curing of urethane acrylate resins based on aliphatic or cyclic isocyanates have good characteristics such as mechanical properties, chemical resistance to solvents, gloss, flow properties, and light-stability. For example, urethane acrylates based on isophorone diisocyanate are known, from German OS No. 29 05 205.
However, such films and coatings have unsatisfactory wear characteristics and defective adhesion, particularly when applied to substrates comprised of plastic material.
It is well known that various thio compounds substantially increase adhesion properties of films if added to the resin before curing.
However, a disadvantage lies in the fact that the thio compounds impart an appreciable noxious odor to the liquid resins as well as to the cured coatings. Moreover, the toxicological aspects must be taken into account as well.
Attempts have been made at improving the adhesion of the coating by substantially tempering the radiation-cured coating at temperatures above 100.degree. C. Curing times of c. 20 to 30 min have been used and have been found to be rather ineffective and impracticable.
Other proposals have been advanced for producing a high coating adhesion with low loss of volume of the liquid resin after curing, but these have not been shown conclusively to be of value.
Thus, a need continues to exist for films and coatings obtained after radiation curing which form well adhering, solvent resistant coatings with excellent wear properties, and which also have an extremely high shelf life.